1. Field of the Invention
This invention relates to laser beam steering and more particularly laser beam steering using Fabry-Perot cells.
2. Description of the Related Art
High-resolution large-angle laser beam steering is increasingly required for a variety of applications, including free-space laser communication, laser radar, target illumination, laser countermeasures, and remote optical sensing. Alternately called dielectric mirrors, filters or thin-film filters, these components are often used to steer laser beams by reflection because of the minimal energy absorption and higher energy tolerance associated with such mirrors, in comparison with metallic mirrors. They have high reflection coefficients over wide bandwidths and are a 1-D subset of a more general class of 3-, 2-, or 1-dimensional periodically structured dielectrics, otherwise known as photonic bandgap (PBG) materials. Light having wavelengths in the band gap is strongly reflected. Formed from a multi-layer stack of dielectric substances with alternating high/low indexes of refraction, the stack may reflect 99% of the laser photons, with the remaining 1% mostly transmitted, rather than absorbed. For such stacks, the width of the reflection band is a significant fraction (for example, >5%) of the center wavelength of the reflection band. The ability to steer laser beams over large elevation and azimuth angles, with minimum mechanical movements, without cascading multiple steering stages and with fast response times presents technical challenges, however. Other technical challenges include designing for cost efficient manufacturing and design scalability to allow a wide beam diameter.
Typical beam steering solutions include angular rotation of reflectors, gratings or holograms, sometimes arranged as rotating polygons, for beam steering in one dimension, or a cascade of multiple elements to scan in two dimensions (x-y, or azimuth and elevation). Beam steering units on mobile platforms often are mechanical gimbals with rotating prisms or lens movements, cascaded for two-dimensional steering, and separate elements for fine and coarse angle steering. Those solutions tend to suffer from being large, heavy, and having slow response times. Many non-gimbaled approaches have been developed, such as a combination of lenses, rotating prisms or lens arrays, acousto-optic, electro-optic, micro-mechanical cantilevers, and more, each with their own limitations, particularly in terms of achieving large angle, two-dimensional laser beam steering. A particular characteristic has been the requirement for using two-stage cascades of one-dimensional beam steering elements to span large angle X-y, or azimuth and elevation angles. One non-gimbaled single-stage 2-dimensional beam steering solution is taught by M. Khoshnevisan in U.S. Pat. No. 6,751,009 (“the '009 patent”). The '009 patent teaches the combination of an acousto-optic fine scan and micro-optic deflectors to provide agile gimballess coarse beam steering over large angles. The micro-optic deflector includes at least two micro-lens arrays disposed adjacent one another with the micro-lens arrays being micro-translatable in X and/or Y directions relative to one another. Unfortunately, several features are not ideal, including the requirement for very high quality microlens arrays for large-angle steering, and limited scalability of the design for larger beam diameters.
A need still exists, therefore, for laser beam steering in a compact and affordable package that is scalable for larger beam widths while maintaining fast response times.